# Speed Control of Stepper Motor Using 8051 Microcontroller

2071 WordsJan 4, 20139 Pages
cc o s ts u c t uoc t i o n onn rt r i n stEPPEr Motor controL usinG 89c51 MicrocontroLLEr Mandeep Singh Walia H ere’s a stepper motor controller based on 89C51 microcontroller to control the rotation of a DC stepper motor in clockwise and anti-clockwise directions. The controller is simple and easy-to-construct, and can be used in many applications including machine control and robotics for controlling the axial rotation in XY plane. A similar circuit can be added to control the rotation of the motor in either XZ or YZ plane. Fig. 1 shows the block diagram of the stepper motor control system. The power supply section (in Fig. 2) consists of a stepdown transformer (7.5V AC, 1A), bridge rectifier (comprising diodes D1 through D4), filter…show more content…
Clock and reset circuit. Two 33pF capacitors (C4 and C5) are connected to pins 18 and 19 of the microcontroller, respectively, with an 11.059MHz piezoelectric crystal (XTAL1) across them. The construction clock frequency of the microcontroller depends on the frequency of the crystal oscillator used. Typically, the maximum and minimum frequencies are 1 MHz and 16 MHz, respectively, so we should use a piezoelectric crystal with a frequency in this range. The speed of the stepper motor is proportional to the frequency of the input pulses or it is inversely proportional to the time delay between pulses, which can be achieved through software by making use of instruction execution time. The time taken by any instruction to get executed can be computed as follows: C×12 Time= F where ‘C’ is the number of cycles an instruction takes to execute and ‘F’ is the crystal frequency. The crystal frequency in this circuit is 11.059 MHz, so the time taken to execute, say, ADD A, R1 (single-cycle instruction), is about one microsecond (µs). Use of a 6MHz crystal will bring down the instruction execution speed to to 2 µs. When power is applied, the reset input must first go high and then low. A resistorcapacitor combination (R1-C3) is used to achieve this until the capacitor begins to charge. At a threshold of about 2.5V, the reset input reaches a low level and the microcontroller begins to function normally.